This is hard to write about, and hard for business owners to accept. It seems so negative. Still, it seems like we all need a fresh reminder. Bill Cosby said it well: “I don’t know the secret to success, but I do know that the secret to failure is trying to please everybody.”

This reminds me, brilliantly, of how important it is to understand . . .

You need customers. The first thing you need to start a business, maybe even the only thing you really need, is customers. It all starts with at least one customer.

Who is your target customer. In detail. Not just generalities and demographics, not even just psychographics, but who is this person, what drives her, what does she really want from you, what does she like to read, eat, watch? Where does he live, and with whom? What does he drive?

Who isn’t your customer. Sometimes the secret to success is who isn’t your customer.

I was in a panel presentation not long ago alongside an expert in customer service. At one point, after she’d dizzied us with stories of Nordstrom retail clerks changing customers’ tires and taking as returns products that Nordstrom had never carried, somebody asked, with just a hint of exasperation, “But how does a company stay in business like that? How do they make money? Who pays for all that?”

At which point, after a beautifully-timed pause, the expert said: “Yes, that is the question, isn’t it . . . and pay attention, because this is the most important thing I’ll say all night . . . you have to understand that not everybody is a customer.”

John Jantsch, in Duct Tape Marketing, recommends that you start by profiling your ideal customer. Focus for a while on one person, whether he or she is your customer directly or the decision-maker for a business customer. Give that person age, gender, income level, likes, dislikes, favorite movies, songs, magazines, restaurants. Know that person.

If you’ve been in business, you can think of that customer fairly easily. Maybe it’s a composite of several real customers.

A clear example of knowing who is and who isn’t your customer can be found in the automobile industry. In theory, everyone who is over 16 years old and has a valid driver’s license could be considered the target customer. But, if you take time to appreciate the ads for different vehicles you’ll see that the marketing efforts are precisely pitched to narrow target markets.

For instance, the rich, deep, saturated colors, focus on high-quality features and refined accessories, the calm and quiet voice, and the sense of genteel conviviality of the Lincoln Town Car speaks directly to the well-heeled buyer. On the other hand, the spinning tires, clouds of smoke, screaming engine and 150 images a minute visual stimulation of an 800 horsepower, street-legal hot-rod TV spot is crafted especially for the hyper-active, quadruple-shot-enhanced-caffeine-energy-drink-quaffing youth.

Other industries segment their target markets. Some restaurants appeal to people in a hurry, or people on a budget, or people looking for a romantic rendezvous, or people who appreciate and seek out the taste treats presented by culinary masters. Every successful restaurant has carefully decided who their target customers are, and who they are not, and then manage their marketing efforts accordingly.

Whole Foods Market and PC Market of Choice are both grocery stores which specialize in organic prepared foods and locally grown organic fruits and vegetables. Their target market customers choose to spend more when buying groceries to get the benefits from healthier foods. Safeway or Kroger or Publix stores on the other hand focus on selling national brands, and target a different, often budget conscious, segment of the population.

A fast-food restaurant knows that the relatively well-to-do baby boomer empty nesters aren’t their customers. On average. The sushi restaurant knows that the construction worker driving a pickup truck who eats at the Texas barbecue drive-through isn’t its customer.

Consider Jolt cola. All the sugar and twice the caffeine. How important is understanding who isn’t the customer.

Your blog, if you’re doing a blog as a business, needs a focus. People don’t care about your inner angst, but there are specialty niche areas all over the place. Old Volkswagen maintenance. Arranging dry flowers. The narrower you cut it the better. Sure there are some general blogs that work, but they started years before you did. Nowadays you need to focus.

It is imperative that you know your customers, and do adequate market research.